1. Field of the Disclosure
The present disclosure relates to the field of semiconductor manufacturing, and more particularly to a wafer-level packaging method of BSI image sensors.
2. Description of Related Art
With continued progress of the chip manufacturing technology and the dedicated imaging technology, development of image sensor using Front Side Illumination (FSI) technology is promoted. As the human eye, when the light falls on the front of the chip of the FSI image sensor, the light will be finally converged to an optical-sensing region by reading circuits and interconnections. FSI technology is currently a mainstream image sensor technology, and has been confirmed by large production capacity, high reliability and high yield as well as an attractive price and other advantages. The FSI technology has been greatly promoted to be applied in mobile phones, laptop computers, digital vidicons and digital cameras and many other fields.
As the electronics industry trends towards compact size, the corresponding chip package also occurs a big change. Over the past thirty years, innovations of concentrating technology and semiconductor manufacturing technology had a significant impact to the pixel size of the image sensors. For example, the pixel size of the image sensor applied in the first portable vidicon is 2.5 microns, but now, the pixel size of the sensor applied in the mobile cameras is only 1.4 microns. Currently, the market demand for the pixel size is small to 1.1 microns, or even 0.65 microns.
Keeping the same wavelength of light while continually shrinking the pixel size, the FSI image sensors appear their physical limitations. In order to solve this problem, a BSI (backside illumination) technology is currently applied in the image sensors as shown in FIG. 1, which effectively removes the read circuit and interconnects on the optical path. Since the BSI image sensors have potential advantages of achieving higher quantum efficiency, the prospects thereof are very attractive.
Referring to FIG. 1, the BSI image sensor 100 includes an image sensing region 1, an interconnection layer 2, a thin silicon layer (not shown), a flat layer 3 and a substrate 4. The image sensing region 1 includes a microlens 11, a filter 12, an optical-sensing region 13 and a pixel region 14. The optical-sensing region 13 is adapted for converting an optical signal into an electrical signal. The optical-sensing region 13 includes a photodiode. The pixel region 14 is used to amplify the electrical signal converted by the photodiode and then output. In order to achieve higher pixel and effectiveness, the interconnection layer 2 of the BSI image sensor is made of a low dielectric constant material (low-k material) and a conductive metal, which can be used to output the electrical signals generated by the BSI image sensor.
However, because the low dielectric constant material is relatively brittle, when using the existing wafer-level packaging process to cut and obtain a plurality of independent BSI image sensors, it is easy to cause cracking of the interconnection layer 2 and let the external water vapor erode the BSI image sensor. Besides, due to special characteristics of the thin silicon layer, once its stress is not well released, reliability thereof might become poor. Furthermore, with the thin silicon layer exposed to the air, the reliability thereof will be greatly decreased. As a result, performance and reliability of the BSI image sensor are greatly influenced.